How to reproduce:
1. Create a new project
2. Create a new Material (by pressing the plus icon in the top left corner of the Project window and selecting "Material")
3. In the Inspector window open the "Shader" dropdown
4. Observe the amount and names of categories

Expected result: There are shader categories and shaders listed in the dropdown, like: AR, FX, GUI, Legacy Shaders, Mobile, Nature, Standard, etc.
Actual result: There is a single category in the dropdown called "Failed to compile"

Reproducible with: 2020.1.0a23
Not reproducible with: 2017.4.37f1, 2018.4.17f1, 2019.3.2f1, 2020.1.0a22

Note: Although shaders are listed in a different category than in versions before 2020.1.0a23 their functionality is unaffected